Scribe line alignment marks are used in the fabrication of integrated circuitry to precisely align the substrates with respect to reticles which are used to pattern the substrates. At least two of such marks are placed within scribe line area of the substrate between integrated circuit die area. Each alignment mark typically includes a plurality of raised and/or lowered features for which a stepper/scanner can optically search to determine and/or modify x-y alignment of the substrate for subsequent processing. The individual spaced features within an alignment mark are typically spaced rectangles, although any configuration might alternately be used.
X-y substrate alignment may occur by direct or indirect methods. With indirect alignment, scribe line alignment marks are initially formed relative to a substrate. Multiple layers are separately provided thereover and may be separately lithographically patterned. In doing so, each time the substrate is x-y aligned, reference may be made to the initially formed alignment marks. Such a method is referred to as “indirect” as each succeeding layer is not referenced to the immediately preceding layer. There are, however, certain critical mask levels which should be patterned relative to an immediately underlying layer. Accordingly, scribe line alignment marks may be fabricated relative to an immediate underlying layer and x-y alignment determined therefrom before patterning a subsequent layer. Such is referred to as “direct alignment”.
The continuing reduction in the feature sizes of circuit components places ever greater demands on the techniques used to form those features. Photolithography is still commonly used to form patterned features such as conductive lines. A concept commonly referred to as “pitch” can be used to describe the sizes of the features in conjunction with spaces immediately adjacent thereto. Pitch may be defined as the distance between an identical point in two neighboring features of a repeating pattern in a straight line cross-section, thereby including the maximum width of the feature and the space to the next immediately adjacent feature. However, due to factors such as optics and light or radiation wave length, photolithography techniques tend to have a minimum pitch below which a particular photolithographic technique cannot reliably form features. Thus, minimum pitch of a photolithographic technique is an obstacle to continued feature size reduction using photolithography.
Pitch doubling or pitch multiplication is one method which extends the capabilities of photolithographic techniques beyond their minimum pitch. Such forms featured narrower than minimum photolithography resolution by depositing spacer-forming layers to have a lateral thickness (width) which is less than that of the minimum capable photolithographic feature size. The spacer-forming layers are then anisotropically etched to form sub-lithographic width features, and then the features which were formed at the minimum photolithographic feature size are etched from the substrate.
In forming scribe line alignment marks where sub-lithographic pitch multiplied features are formed, such may result in very narrow width features on the order of 50 nanometers and less that may be spaced more than a thousand nanometers apart. This makes it difficult or impossible for the scanners to view such features of scribe line alignment marks, thus precluding use of direct alignment techniques unless separate, dedicated masking for alignment marks is used.
While the invention was motivated in addressing the above-identified issues, the invention is in no way limited in overcoming some or all of the above-identified drawbacks. Rather, the invention is encompassed by the accompanying claims as literally worded and in accordance with the doctrine of equivalents.